Hand operable pliers including a pliers head are known from German Patent Application No. 198 07 737 A1 corresponding to U.S. Pat. No. 6,026,671. The known pliers head includes two cover plates having the shape of a “C” to form a C-shaped mouth or opening. The C-shape is required to insert work pieces from one side, or to be capable of using the pliers head at work pieces which are continuous in a direction perpendicular with respect to the plane of main extension of the pliers head. In the known pliers head, two dies are arranged in the region of the C-shaped mouth. The dies are designed and arranged to be replaceable. The first die is designed as a stationary die, and the second die is designed to be movable by a drive. The movable die is linearly guided in straight channels being located in the cover plates. A toggle lever drive serves to linearly drive the movable die. With the known pliers including a pliers head, it is desired to achieve improved tilting resistance of the movable die. This result is achieved by the guiding protrusions being located at the C-shaped mouth have a great basis for the linearly movable die. In this way, reproducible precision of the pressing quality and tilt resistance of the linear guidance of the movable die are improved such that the crimping quality is increased.
In addition to the improvement concerning the linear guidance of the movable crimping die, it is also known from German Patent Application No. 198 07 737 A1 and U.S. Pat. No. 6,026,671 that pliers heads having a C-shaped mouth generally have the drawback of the correspondingly C-shaped cover plates showing resilient effects when great pressing forces are applied. Despite the linear guidance of the movable pressing die, the two pressing dies reach an angled position which not only has a negative influence on the pressing quality, but which also leads to early wear and tear of the pressing dies. Due to the resilient effects of the cover plates within a certain but limited angle, undesired pressing marks may occur in the nests of the dies. These pressing marks result in undesired changes of the nests. Consequently, in the case of a C-shaped design of the pliers head, it is preferred to counteract resilient effects of the pliers head especially during great pressing forces by the arrangement of additional stiffening plates. The stiffening plates may be added to the covering plates to increase stiffness of the C-shaped mouth and to counteract resilient effects. Especially in the case of hand driven tools such as hand operable pliers, the possibilities of increasing the mass in the region of the C-shaped opening and of designing a C-shaped mouth as a stiff and non-resilient body are limited. In many cases, it is not possible to arrange stiffening plates in the pliers head since adjusting units and the like for determining the pressing position of the work piece are located in this region.
In addition to the arrangement of stiffening plates, German Patent Application No. 198 07 737 A1 and U.S. Pat. No. 6,026,671 also teach to associate a pivoting element with the C-shaped mouth. The pivoting element serves to close the opening of the C-shaped mouth. In this way, resilient effects of the C-shaped mouth are counteracted.